Method of depositing ammonia free and chlorine free conformal silicon nitride film

ABSTRACT

Provided herein are methods of depositing conformal silicon nitride films using atomic layer deposition by exposure to a halogen-free, N—H-bond-free, and carbon-free silicon-containing precursor such as disilane, purging of the precursor, exposure to a nitrogen plasma, and purging of the plasma at low temperatures. A high frequency plasma is used, such as a plasma having a frequency of at least 13.56 MHz or at least 27 MHz. Methods yield substantially pure conformal silicon nitride films suitable for deposition in semiconductor devices, such as in trenches or features, or for memory encapsulation.

BACKGROUND

Silicon nitride (SiN) thin films have unique physical, chemical andmechanical properties and thus are used in a variety of applications,particularly semiconductor devices, for example in diffusion barriers,gate insulators, sidewall spacers, encapsulation layers, strained filmsin transistors, and the like. Conventional SiN films have been depositedat relatively high temperatures, such as in Front End of Line (FEOL)applications. For example, SiN films are typically deposited by chemicalvapor deposition (CVD) in a reactor at temperatures greater than 750° C.using dichlorosilane and ammonia. However, as SiN films are used inlate-stage semiconductor fabrication processes, and as device dimensionscontinue to shrink, there is an increasing demand for SiN films to beformed at lower temperatures, for example less than 600° C.

SUMMARY

Provided herein are methods of depositing silicon nitride films. Oneaspect includes a method of depositing a silicon nitride film on asubstrate in a chamber by (a) exposing the substrate to asilicon-containing precursor under conditions allowing formation of anadsorbed layer of the silicon containing precursor on the substratesurface, and (b) exposing the adsorbed layer to a nitrogen (N₂) plasmato thereby form a silicon nitride film, where the silicon-containingprecursor is N—H bond-free. In some embodiments, the silicon-containingprecursor is halide-free. In some embodiments, the silicon-containingprecursor is carbon-free. In various embodiments, a carrier gas isflowed throughout (a) through (b). In some embodiments, the carrier gasis hydrogen-free.

In some embodiments, the silicon-containing precursor is selected fromthe group consisting of silane, disilane, trisilane, tetrasilane, andtrisilylamine. In some embodiments, the silicon-containing precursor hasa silicon to hydrogen ratio between about 12:4 and about 12:5. Invarious embodiments, the process temperature is less than about 250° C.

The method may also include (c) repeating (a)-(b), and (d) periodicallyexposing the substrate to a hydrogen-containing plasma. The substratemay be exposed to the hydrogen-containing plasma for a time betweenabout 0.05 seconds and about 60 seconds.

In some embodiments, exposing the substrate to the hydrogen-containingplasma includes exposing the substrate to a hydrogen-containing gas andigniting a plasma, where the hydrogen-containing gas is selected fromthe group consisting of ammonia, hydrogen, and combinations thereof.

In various embodiments, the frequency of the plasma is at least about13.56 MHz. In some embodiments, the frequency of the plasma is about 27MHz.

In some embodiments, the silicon containing precursor is adsorbed ontoless than about 60% of the substrate surface. The adsorbed layer on thesubstrate surface in (a) may be less than about 0.5 Å thick.

Another aspect includes a method of depositing a silicon nitride film ona substrate in a chamber by (a) exposing the substrate to asilicon-containing precursor under conditions under conditions allowingformation of an adsorbed layer of the silicon containing precursor onthe substrate surface, and (b) exposing the adsorbed layer to a nitrogen(N₂) plasma to thereby form a silicon nitride film, where thesilicon-containing precursor comprises at least about 75% nonpolarcovalent bonds. In some embodiments, the silicon-containing precursor istrisilylamine.

The method may also include (c) repeating (a)-(b), and (d) periodicallyexposing the substrate to a hydrogen-containing plasma. The substratemay be exposed to the hydrogen-containing plasma for a time betweenabout 0.05 seconds and about 60 seconds.

In some embodiments, exposing the substrate to the hydrogen-containingplasma includes exposing the substrate to a hydrogen-containing gas andigniting a plasma, where the hydrogen-containing gas is selected fromthe group consisting of ammonia, hydrogen, and combinations thereof. Invarious embodiments, the adsorbed layer on the substrate surface in (a)is less than about 0.5 Å thick.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram depicting operations for a method inaccordance with disclosed embodiments.

FIG. 2 is a timing sequence diagram showing an example of cycles in amethod in accordance with disclosed embodiments.

FIG. 3 is a schematic diagram of an example process station forperforming disclosed embodiments.

FIG. 4 is a schematic diagram of an example process tool for performingdisclosed embodiments.

FIG. 5 is a Fourier transform infrared spectrum of films fromexperimental data.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Silicon nitride may be used in semiconductor device fabrication asdiffusion barriers, gate insulators, sidewall spacers, and encapsulationlayers. In particular, in some semiconductor devices, a carbon layer maybe deposited on a phase change layer that is modified when heated. Whenheated, a damaged phase change layer may not change phases. This phasechange layer may also be sensitive to light. To prevent any damage tothe phase change layer, a conformal memory encapsulation layer, whichmay be silicon nitride, is deposited on the phase change layer. Thememory encapsulation has little to no contamination of other compoundsand is deposited at low temperatures to avoid damaging the device.Conformal silicon nitride layers may also be used in other applications.

Provided herein are methods of depositing conformal silicon nitride byatomic layer deposition (ALD) using high molecular weight, halogen-free,carbon-free silicon-containing precursors, and nitrogen plasma. In someembodiments, the precursors are also free of N—H bonds. The term“nitrogen plasma” as used herein should be understood to mean plasmagenerated by igniting nitrogen (N₂) gas with a remote or in-situ plasmagenerator. The deposited silicon nitride films have little to no carboncontamination, and no halogen contamination.

The deposited films may be highly conformal. Conformality of films maybe measured by the step coverage. Step coverage may be calculated bycomparing the average thickness of a deposited film on a bottom,sidewall, or top of a feature to the average thickness of a depositedfilm on a bottom, sidewall, or top of a feature. For example, stepcoverage may be calculated by dividing the average thickness of thedeposited film on the sidewall by the average thickness of the depositedfilm at the top of the feature and multiplying it by 100 to obtain apercentage.

The methods provided herein involve deposition by ALD. Unlike a chemicalvapor deposition (CVD) technique, ALD processes use surface-mediateddeposition reactions to deposit films on a layer-by-layer basis. In oneexample of an ALD process, a substrate surface, including a populationof surface active sites, is exposed to a gas phase distribution of afirst precursor, such as a silicon-containing precursor, in a doseprovided to a process station housing the substrate. Molecules of thisfirst precursor are adsorbed onto the substrate surface, includingchemisorbed species and/or physisorbed molecules of the first precursor.It should be understood that when the compound is adsorbed onto thesubstrate surface as described herein, the adsorbed layer may includethe compound as well as derivatives of the compound. For example, anadsorbed layer of a silicon-containing precursor may include thesilicon-containing precursor as well as derivatives of thesilicon-containing precursor. In certain embodiments, an ALD precursordose partially saturates the substrate surface. In some embodiments, thedose phase of an ALD cycle concludes before precursor contacts thesubstrate to evenly saturate the surface. Typically, the precursor flowis turned off or diverted at this point, and only purge gas flows. Byoperating in this sub-saturation regime, the ALD process reduces thecycle time and increases throughput. However, because precursoradsorption is not saturation limited, the adsorbed precursorconcentration may vary slightly across the substrate surface. Examplesof ALD processes operating in the sub-saturation regime are provided inU.S. patent application Ser. No. 14/061,587, filed Oct. 23, 2013, titled“SUB-SATURATED ATOMIC LAYER DEPOSITION AND CONFORMAL FILM DEPOSITION,”which is incorporated herein by reference in its entirety. After a firstprecursor dose, the reactor is then evacuated to remove any firstprecursor remaining in gas phase so that only the adsorbed speciesremain. A second reactant, such as a nitrogen-containing reactant, isintroduced to the reactor so that some of these molecules react with thefirst precursor adsorbed on the surface. In some processes, the secondprecursor reacts immediately with the adsorbed first precursor. In otherembodiments, the second precursor reacts only after a source ofactivation is applied temporally. The reactor may then be evacuatedagain to remove unbound second precursor molecules. Additional ALDcycles may be used to build film thickness.

In some implementations, the ALD methods include plasma activation. Asdescribed herein, the ALD method and apparatuses described herein may beconformal film deposition (CFD) methods, which are described generallyin U.S. patent application Ser. No. 13/084,399 (now U.S. Pat. No.8,728,956), filed Apr. 11, 2011, and titled “PLASMA ACTIVATED CONFORMALFILM DEPOSITION,” and in U.S. patent application Ser. No. 13/084,305,filed Apr. 11, 2011, and titled “SILICON NITRIDE FILMS AND METHODS,”which are herein incorporated by reference in its entireties.

Disclosed embodiments include methods that form an adsorbed layer of thesilicon precursor that is sufficiently reactive to react with nitrogenplasma at low temperatures. Methods include atomic layer deposition(ALD) processes in which a silicon precursor is adsorbed onto asubstrate surface. In many embodiments, the methods disclosed may beperformed at a temperature less than about 250° C., such as about 200°C. In some embodiments, the pedestal is set to a temperature of lessthan about 250° C. In some embodiments, the method is performed at ahigher temperature, such as greater than about 250° C., or greater than300° C. In general, a higher deposition temperature results in higherstep coverage, but temperature may be limited by the device to avoiddamaging any existing layers on the device. In various embodiments, themethods may be performed at a pressure between about 0.1 Torr and about20 Torr. In the following example, flow rates are provided for a 180 Lchamber, which may include a number of process stations. In some cases,depending on the reactor configuration, the flow rates may be scaled toaccommodate different volumes. Embodiments described herein may alsooperate at higher frequency plasmas, which help form a silicon nitridefilm with a lower wet etch rate. In many embodiments, silicon nitridefilms are deposited in ALD cycles as described herein.

FIG. 1 is an example of a process flow diagram depicting operations forperforming methods in accordance with disclosed embodiments. FIG. 2 is atiming sequence diagram of example pulses in accordance with disclosedembodiments. FIG. 2 shows phases in an example ALD process 200, forvarious process parameters, such as carrier gas flow, silicon-precursorflow, plasma, and nitrogen flow. In FIG. 2, argon is indicated as anexample carrier gas and disilane represents an example of asilicon-precursor. The lines indicate when the flow or plasma is turnedon and off, accordingly. Example process parameters include, but are notlimited to, flow rates for inert and reactant species, plasma power andfrequency, substrate temperature, and process station pressure. FIGS. 1and 2 will be described together below.

In operation 101 of FIG. 1, a substrate is provided to a processstation. The substrate may be a silicon wafer, e.g., a 200-mm wafer, a300-mm wafer, or a 450-mm wafer, including wafers having one or morelayers of material, such as dielectric, conducting, or semi-conductingmaterial deposited thereon. Substrates may have “features” such as viaor contact holes, which may be characterized by one or more of narrowand/or re-entrant openings, constrictions within the feature, and highaspect ratios. The feature may be formed in one or more of the abovedescribed layers. One example of a feature is a hole or via in asemiconductor substrate or a layer on the substrate. Another example isa trench in a substrate or layer. In various embodiments, the featuremay have an under-layer, such as a barrier layer or adhesion layer.Non-limiting examples of under-layers include dielectric layers andconducting layers, e.g., silicon oxides, silicon nitrides, siliconcarbides, metal oxides, metal nitrides, metal carbides, and metallayers.

In some embodiments, the feature may have an aspect ratio of at leastabout 2:1, at least about 4:1, at least about 6:1, at least about 10:1,or higher. The feature may also have a dimension near the opening, e.g.,an opening diameter or line width of between about 10 nm to 500 nm, forexample between about 25 nm and about 300 nm. Disclosed methods may beperformed on substrates with features having an opening less than about150 nm. A feature via or trench may be referred to as an unfilledfeature or a feature. A feature that may have a re-entrant profile thatnarrows from the bottom, closed end, or interior of the feature to thefeature opening.

During operations 103-109 of FIG. 1, an inert gas may be flowed. Invarious embodiments, the inert gas is used as a carrier gas. Examplecarrier gases include argon (Ar), helium (He), and neon (Ne). In someembodiments, the carrier gas is not hydrogen, such that little to nohydrogen is incorporated into the deposited silicon nitride film. Insome embodiments, a hydrogen-containing carrier gas may be used. Theexample sequence in FIG. 2 uses argon as an example carrier gas, whichis continuously flowed during the entire process. The inert gas may beprovided to assist with pressure and/or temperature control of theprocess chamber, evaporation of a liquid reactant, more rapid deliveryof the reactant and/or as a sweep gas for removing process gases fromthe process chamber and/or process chamber plumbing. In someembodiments, nitrogen may be flowed throughout operations 103-109, andignited as a nitrogen plasma in operation 107 as described below.

In operation 103 of FIG. 1, the substrate is exposed to asilicon-containing precursor that is adsorbed onto the substratesurface. This operation may be part of an ALD cycle. The concept of anALD “cycle” is relevant to the discussion of various embodiments herein.Generally a cycle is the minimum set of operations used to perform asurface deposition reaction one time. The result of one cycle isproduction of at least a partial silicon nitride film layer on asubstrate surface. Typically, an ALD cycle includes operations todeliver and adsorb at least one reactant to the substrate surface, andthen react the adsorbed reactant with one or more reactants to form thepartial layer of film. The cycle may include certain ancillaryoperations such as sweeping one of the reactants or byproducts and/ortreating the partial film as deposited. Generally, a cycle contains oneinstance of a unique sequence of operations. As an example, a cycle mayinclude the following operations: (i) delivery/adsorption of asilicon-containing precursor, (ii) purging of silicon-containingprecursor from the station, (iii) delivery of nitrogen plasma, and (iv)purging of plasma from the station.

Any suitable number of deposition cycles may be included in an ALDprocess to deposit a desired film thickness of silicon nitride. Thetiming sequence in FIG. 2 depicts various operations of FIG. 1 in twodeposition cycles, 210A and 210B. As shown, in each cycle, the substrateis exposed to disilane as described above with respect to operation 103of FIG. 1. For example, during deposition cycle 210A, the substrate isexposed to disilane during the disilane exposure phase 220A, and duringdeposition cycle 210B, the substrate is exposed to disilane during thedisilane exposure phase 220B. Note that during the disilane exposurephases 220A and 220B, the plasma is turned off, no nitrogen is flowed tothe station, and the carrier gas, such as argon, continues to flow. Thesubstrate may be exposed to the silicon-containing precursor for a timebetween about 0.2 seconds and about 6 seconds, depending on the flowrate and the substrate surface area.

Returning to FIG. 1, during operation 103, the substrate is exposed tothe silicon-containing precursor such that the silicon-containingprecursor is adsorbed onto the substrate surface to form an adsorbedlayer. In some embodiments, the silicon-containing precursor adsorbsonto the substrate surface in a self-limiting manner such that onceactive sites are occupied by the silicon-containing precursor, little orno additional silicon-containing precursor will be adsorbed on thesubstrate surface. For example, silicon-containing precursors may beadsorbed onto about 60% of the substrate surface. In variousembodiments, when the silicon-containing precursor is flowed to thestation, the silicon-containing precursor adsorbs onto active sites onthe surface of the substrate, forming a thin layer of thesilicon-containing precursor on the surface. In various embodiments,this layer may be less than a monolayer, and may have a thicknessbetween about 0.2 Å and about 0.4 Å. Methods provided herein may beperformed at a temperature less than about 450° C. At processtemperatures greater than about 450° C., some silicon-containingprecursors may decompose to form a layer of silicon.

Unlike a CVD or CVD-like process, the silicon-containing precursor doesnot decompose to form a silicon layer. In various embodiments, operation103 is performed such that not all active sites are occupied by asilicon-containing precursor.

In some embodiments, the silicon-containing precursor does not includeany N—H bonds, and does not include a primary or secondary amine. Insome embodiments, the silicon-containing precursor has no NH₃ groups. Invarious embodiments, the silicon-containing precursor is halogen-free.In some embodiments, the silicon-containing precursor is carbon-free. Insome embodiments, the silicon-precursor is free of N—H bonds. Thesilicon-containing precursor may also have a hydrogen to silicon atomicratio of between about 12:3 to about 12:5.

Generally, silicon-containing precursors as used in methods describedherein do not have an electron-donating or electron-attracting group.Without being bound by a particular theory, silicon-containingprecursors that do not have electron-donating or electron-attractinggroups may be more reactive to form silicon-nitrogen bonds. In someembodiments, the silicon-containing precursor does not include highlypolar bonds. The adsorbed surface layer of the substrate may includenonpolar covalent bonds extending from the substrate surface to reactwith the plasma. In various embodiments, the silicon-containingprecursor includes more than about 75% nonpolar covalent bonds. Forexample, trisilylamine includes 3 polar covalent Si—N bonds and 9nonpolar covalent Si—H bonds. In some embodiments, the electronegativitydifference between the two atoms at the bonds at the ends of thesilicon-containing precursor is less than 0.5 on the Pauling scale.

Example silicon-containing precursors suitable for use in accordancewith disclosed embodiments include polysilanes (H₃Si—(SiH₂)_(n)—SiH₃),where n≧1, such as silane, disilane, trisilane, tetrasilane; andtrisilylamine:

Returning to FIG. 1, in operation 105, the process station is optionallypurged to remove excess silicon-containing precursor in gas phase thatdid not adsorb onto the surface of the substrate. Purging may involve asweep gas, which may be a carrier gas used in other operations or adifferent gas. In some embodiments, purging may involve evacuating thechamber. Operation 105 of FIG. 1 may correspond with purge phase 240A orpurge phrase 240B of FIG. 2, where the disilane flow is turned off, noplasma is ignited, and no nitrogen is supplied to the station. Thecarrier gas, such as argon, continues to flow to purge any excessdisilane from the station. In some embodiments, purge phase 240A mayinclude one or more evacuation subphases for evacuating the processstation. Alternatively, it will be appreciated that purge phase 240A maybe omitted in some embodiments. Purge phase 240A may have any suitableduration, such as between about 0 seconds and about 60 seconds, or about0.01 seconds. In some embodiments, increasing a flow rate of a one ormore sweep gases may decrease the duration of purge phase 240A. Forexample, a purge gas flow rate may be adjusted according to variousreactant thermodynamic characteristics and/or geometric characteristicsof the process station and/or process station plumbing for modifying theduration of purge phase 240A. In one non-limiting example, the durationof a sweep phase may be adjusted by modulating sweep gas flow rate. Thismay reduce deposition cycle time, which may improve substratethroughput. After a purge, the silicon-containing precursors remainadsorbed onto the substrate surface.

In some embodiments, the substrate may be optionally periodicallyexposed to a hydrogen-containing plasma to selectively inhibitdeposition near the top of a feature. Such exposure may improve theconformality of the deposited film. Exposure to the hydrogen-containingplasma may last between about 0.05 seconds and about 60 seconds. Methodsof using a hydrogen-containing inhibitor to tune conformality in atomiclayer deposition are described in U.S. patent application Ser. No.14/552,011 filed on Nov. 24, 2014 titled “SELECTIVE INHIBITION IN ATOMICLAYER DEPOSITION OF SILICON-CONTAINING FILMS,” (Attorney Docket Number3520-1/LAMRP148), which is herein incorporated by reference in itsentirety.

In operation 107 of FIG. 1, the substrate is exposed to a nitrogenplasma. Accordingly, in FIG. 2, nitrogen flow and the plasma are bothturned on during the nitrogen plasma exposure phase in 260A and 260B forthe deposition cycles 210A and 210B respectively. In some embodiments,nitrogen flow may be turned on prior to turning on the plasma, forexample, to allow the nitrogen flow to stabilize. Note that disilaneflow is turned off during the plasma exposure phases and argon as acarrier gas continues to flow. The substrate may be exposed to thenitrogen plasma for a duration between about 0.1 second and about 6seconds. In some embodiments, nitrogen plasma exposure phase 260A or260B may have a duration that exceeds a time for plasma to interact withall precursors adsorbed on the substrate surface, forming a continuousfilm atop the substrate surface.

In various embodiments, the plasma is an in-situ plasma, such that theplasma is formed directly above the substrate surface in the station.The in-situ plasma may be ignited at a power per substrate area betweenabout 0.2122 W/cm² and about 2.122 W/cm². For example, the power mayrange from about 600 W to about 6000 W for a chamber processing four 300mm wafers. For example, plasmas for ALD processes may be generated byapplying a radio frequency (RF) field to a gas using two capacitivelycoupled plates. Ionization of the gas between plates by the RF fieldignites the plasma, creating free electrons in the plasma dischargeregion. These electrons are accelerated by the RF field and may collidewith gas phase reactant molecules. Collision of these electrons withreactant molecules may form radical species that participate in thedeposition process. It will be appreciated that the RF field may becoupled via any suitable electrodes. Non-limiting examples of electrodesinclude process gas distribution showerheads and substrate supportpedestals. It will be appreciated that plasmas for ALD processes may beformed by one or more suitable methods other than capacitive coupling ofan RF field to a gas. In some embodiments, the plasma is a remoteplasma, such that nitrogen is ignited in a remote plasma generatorupstream of the station, then delivered to the station where thesubstrate is housed.

During operation 107, plasma energy is provided to activate the nitrogengas into ions and radicals, which react with the adsorbed layer ofsilicon-containing precursor. For example, the plasma may directly orindirectly activate the nitrogen gas phase molecules to form nitrogenradicals or ions. Nitrogen radicals, although short-lived, may enter atrench or feature in the substrate to react with the adsorbed layer onthe surface of the substrate. However, step coverage may not be 100% ina single cycle since some nitrogen radicals may be deactivated afterentering a trench or via. Nonetheless, using a nitrogen plasma reducescontamination in the deposited conformal silicon nitride film.

Without being bound by a particular theory, higher frequency plasmas maygenerate more radicals than ions, thereby improving deposition ofsilicon nitride due to higher reactivity between the radicals and thesilicon-containing precursor. The radical density desired during thisoperation therefore depends on the plasma frequency. In variousembodiments, a high frequency plasma is used having a frequency of atleast about 13.56 MHz, or at least about 27 MHz, or at least about 40MHz, or at least about 60 MHz. In some embodiments, having a higher iondensity reduces conformality of the film, but conformality may beimproved using methods described herein.

Once the plasma activates the nitrogen gas, the nitrogen radicals andions react with the silicon-containing precursor adsorbed on the surfaceof the substrate, forming silicon-nitrogen bonds and a thin film ofsilicon nitride. This resulting film is carbon-free and halogen-free dueto the lack of carbons in the chemistry used to deposit these films.

Returning to FIG. 1, in operation 109, the process station is purged. Asshown in FIG. 2, operation 109 may correspond with purge phase 280A orpurge phase 280B, where the disilane flow is turned off, no plasma isignited, and no nitrogen is supplied to the station. The purge may beperformed by flowing the carrier gas, which may be any of thosedescribed above with respect to operation 105. In many embodiments, thecarrier gas used in operation 105 and 109 are the same gas, and in someembodiments, the carrier gas is continuously flowed during theseoperations, such as shown in FIG. 2.

Performing operations 103-109 of FIG. 1 may constitute a cycle, such asdeposition cycle 210A, or deposition cycle 210B in FIG. 2. Depending onthe exposure time of the operations, each cycle may deposit a siliconnitride film having a thickness between about 0.05 Å and about 2 Å. Forexample, deposition at about 250° C. with disilane as a precursor maydeposit about 0.5 Å per cycle. Thus, processes may be time consumingwhen depositing films more than a few nanometers thick. Further, somereactants may have long exposure times to deposit a conformal film,which may also reduce wafer throughput time.

In operation 113, it is determined whether the film has been depositedto an adequate thickness. If not, operations 103-109 may be repeated. Insome repeated cycles, exposure to a hydrogen-containing inhibitor may beused in each cycle or in a selected number of cycles to inhibitdeposition and improve conformality of the deposited silicon nitridelayers. The method depicted in FIGS. 1 and 2 produce conformal siliconnitride films that are carbon-free, since no carbon-containing compoundsare used in the process. These compounds are also halogen-free, becausethe silicon-containing precursors used do not contain halogens. In someembodiments where hydrogen is not used as a carrier gas, there is alsoless incorporation of hydrogen in the silicon nitride film. Filmsdeposited using the disclosed embodiments are suitable for use in manysemiconductor processing applications, such as deposition of memoryencapsulation films, due to their low contamination. Silicon nitridefilms as described herein may also be used as a layer to suppress dilutehydrogen fluoride (HF) wet etch rate and compensate for wet etch ratedegradation due to inherent loss of density at the lower temperaturesused for emerging memory encapsulation layer applications.

Apparatus

FIG. 3 depicts a schematic illustration of an embodiment of an atomiclayer deposition (ALD) process station 300 having a process chamber body302 for maintaining a low-pressure environment. A plurality of ALDprocess stations 300 may be included in a common low pressure processtool environment. For example, FIG. 4 depicts an embodiment of amulti-station processing tool 400. In some embodiments, one or morehardware parameters of ALD process station 300, including thosediscussed in detail below, may be adjusted programmatically by one ormore computer controllers 350.

ALD process station 300 fluidly communicates with reactant deliverysystem 301 a for delivering process gases to a distribution showerhead306. Reactant delivery system 301 a includes a mixing vessel 304 forblending and/or conditioning process gases for delivery to showerhead306. One or more mixing vessel inlet valves 320 may control introductionof process gases to mixing vessel 304.

As an example, the embodiment of FIG. 3 includes a vaporization point303 for vaporizing liquid reactant to be supplied to the mixing vessel304. In some embodiments, vaporization point 303 may be a heatedvaporizer. The saturated reactant vapor produced from such vaporizersmay condense in downstream delivery piping. Exposure of incompatiblegases to the condensed reactant may create small particles. These smallparticles may clog piping, impede valve operation, contaminatesubstrates, etc. Some approaches to addressing these issues involvepurging and/or evacuating the delivery piping to remove residualreactant. However, purging the delivery piping may increase processstation cycle time, degrading process station throughput. Thus, in someembodiments, delivery piping downstream of vaporization point 303 may beheat traced. In some examples, mixing vessel 304 may also be heattraced. In one non-limiting example, piping downstream of vaporizationpoint 303 has an increasing temperature profile extending fromapproximately 100° C. to approximately 150° C. at mixing vessel 304.

In some embodiments, liquid precursor or liquid reactant may bevaporized at a liquid injector. For example, a liquid injector mayinject pulses of a liquid reactant into a carrier gas stream upstream ofthe mixing vessel. In one embodiment, a liquid injector may vaporize thereactant by flashing the liquid from a higher pressure to a lowerpressure. In another example, a liquid injector may atomize the liquidinto dispersed microdroplets that are subsequently vaporized in a heateddelivery pipe. Smaller droplets may vaporize faster than largerdroplets, reducing a delay between liquid injection and completevaporization. Faster vaporization may reduce a length of pipingdownstream from vaporization point 303. In one scenario, a liquidinjector may be mounted directly to mixing vessel 304. In anotherscenario, a liquid injector may be mounted directly to showerhead 306.

In some embodiments, a liquid flow controller (LFC) upstream ofvaporization point 303 may be provided for controlling a mass flow ofliquid for vaporization and delivery to process station 300. Forexample, the LFC may include a thermal mass flow meter (MFM) locateddownstream of the LFC. A plunger valve of the LFC may then be adjustedresponsive to feedback control signals provided by aproportional-integral-derivative (PID) controller in electricalcommunication with the MFM. However, it may take one second or more tostabilize liquid flow using feedback control. This may extend a time fordosing a liquid reactant. Thus, in some embodiments, the LFC may bedynamically switched between a feedback control mode and a directcontrol mode. In some embodiments, this may be performed by disabling asense tube of the LFC and the PID controller.

Showerhead 306 distributes process gases toward substrate 312. In theembodiment shown in FIG. 3, the substrate 312 is located beneathshowerhead 306 and is shown resting on a pedestal 308. Showerhead 306may have any suitable shape, and may have any suitable number andarrangement of ports for distributing process gases to substrate 312.

In some embodiments, a microvolume 307 is located beneath showerhead306. Practicing disclosed embodiments in a microvolume rather than inthe entire volume of a process station may reduce reactant exposure andpurge times, may reduce times for altering process conditions (e.g.,pressure, temperature, etc.) may limit an exposure of process stationrobotics to process gases, etc. Example microvolume sizes include, butare not limited to, volumes between 0.1 liter and 2 liters. This alsoimpacts productivity throughput. In some embodiments, the disclosedembodiments are not performed in a microvolume.

In some embodiments, pedestal 308 may be raised or lowered to exposesubstrate 312 to microvolume 307 and/or to vary a volume of microvolume307. For example, in a substrate transfer phase, pedestal 308 may beraised to position substrate 312 within microvolume 307. In someembodiments, microvolume 307 may completely enclose substrate 312 aswell as a portion of pedestal 308 to create a region of high flowimpedance.

Optionally, pedestal 308 may be lowered and/or raised during portionsthe process to modulate process pressure, reactant concentration, etc.,within microvolume 307. In one scenario where process chamber body 302remains at a base pressure during the process, lowering pedestal 308 mayallow microvolume 307 to be evacuated. Example ratios of microvolume toprocess chamber volume include, but are not limited to, volume ratiosbetween 1:500 and 1:10. It will be appreciated that, in someembodiments, pedestal height may be adjusted programmatically by asuitable computer controller 350.

In another scenario, adjusting a height of pedestal 308 may allow aplasma density to be varied during plasma activation cycles included inthe process. At the conclusion of the process phase, pedestal 308 may belowered during another substrate transfer phase to allow removal ofsubstrate 312 from pedestal 308.

While the example microvolume variations described herein refer to aheight-adjustable pedestal 308, it will be appreciated that, in someembodiments, a position of showerhead 306 may be adjusted relative topedestal 308 to vary a volume of microvolume 307. Further, it will beappreciated that a vertical position of pedestal 308 and/or showerhead306 may be varied by any suitable mechanism within the scope of thepresent disclosure. In some embodiments, pedestal 308 may include arotational axis for rotating an orientation of substrate 312. It will beappreciated that, in some embodiments, one or more of these exampleadjustments may be performed programmatically by one or more suitablecomputer controllers 350.

In some embodiments where plasma may be used as discussed above,showerhead 306 and pedestal 308 electrically communicate with a radiofrequency (RF) power supply 314 and matching network 316 for powering aplasma. In some embodiments, the plasma energy may be controlled bycontrolling one or more of a process station pressure, a gasconcentration, an RF source power, an RF source frequency, and a plasmapower pulse timing. For example, RF power supply 314 and matchingnetwork 316 may be operated at any suitable power to form a plasmahaving a desired composition of radical species. Examples of suitablepowers are included above. Likewise, RF power supply 314 may provide RFpower of any suitable frequency. In some embodiments, RF power supply314 may be configured to control high- and low-frequency RF powersources independently of one another. Example low-frequency RFfrequencies may include, but are not limited to, frequencies between 0kHz and 500 kHz. Example high-frequency RF frequencies may include, butare not limited to, frequencies between 1.8 MHz and 2.45 GHz, or greaterthan about 13.56 MHz, or greater than 27 MHz, or greater than 40 MHz, orgreater than 60 MHz. It will be appreciated that any suitable parametersmay be modulated discretely or continuously to provide plasma energy forthe surface reactions. In one non-limiting example, the plasma power maybe intermittently pulsed to reduce ion bombardment with the substratesurface relative to continuously powered plasmas.

In some embodiments, the plasma may be monitored in-situ by one or moreplasma monitors. In one scenario, plasma power may be monitored by oneor more voltage, current sensors (e.g., VI probes). In another scenario,plasma density and/or process gas concentration may be measured by oneor more optical emission spectroscopy sensors (OES). In someembodiments, one or more plasma parameters may be programmaticallyadjusted based on measurements from such in-situ plasma monitors. Forexample, an OES sensor may be used in a feedback loop for providingprogrammatic control of plasma power. It will be appreciated that, insome embodiments, other monitors may be used to monitor the plasma andother process characteristics. Such monitors may include, but are notlimited to, infrared (IR) monitors, acoustic monitors, and pressuretransducers.

In some embodiments, instructions for a controller 350 may be providedvia input/output control (IOC) sequencing instructions. In one example,the instructions for setting conditions for a process phase may beincluded in a corresponding recipe phase of a process recipe. In somecases, process recipe phases may be sequentially arranged, so that allinstructions for a process phase are executed concurrently with thatprocess phase. In some embodiments, instructions for setting one or morereactor parameters may be included in a recipe phase. For example, afirst recipe phase may include instructions for setting a flow rate ofan inert and/or a reactant gas (e.g., the first precursor such asdisilane), instructions for setting a flow rate of a carrier gas (suchas argon), and time delay instructions for the first recipe phase. Asecond, subsequent recipe phase may include instructions for modulatingor stopping a flow rate of an inert and/or a reactant gas, andinstructions for modulating a flow rate of a carrier or purge gas andtime delay instructions for the second recipe phase. A third recipephase may include instructions for setting a flow rate of an inertand/or reactant gas which may be the same as or different from the gasused in the first recipe phase (e.g., the plasma reactant such asnitrogen), instructions for modulating a flow rate of a carrier gas, andtime delay instructions for the third recipe phase. A fourth recipephase may include instructions for modulating or stopping a flow rate ofan inert and/or a reactant gas, instructions for modulating the flowrate of a carrier or purge gas, and time delay instructions for thefourth recipe phase. It will be appreciated that these recipe phases maybe further subdivided and/or iterated in any suitable way within thescope of the present disclosure.

In some embodiments, pedestal 308 may be temperature controlled viaheater 310. Further, in some embodiments, pressure control for processstation 300 may be provided by butterfly valve 318. As shown in theembodiment of FIG. 3, butterfly valve 318 throttles a vacuum provided bya downstream vacuum pump (not shown). However, in some embodiments,pressure control of process station 300 may also be adjusted by varyinga flow rate of one or more gases introduced to the process station 300.

As described above, one or more process stations may be included in amulti-station processing tool. FIG. 4 shows a schematic view of anembodiment of a multi-station processing tool 400 with an inbound loadlock 402 and an outbound load lock 404, either or both of which mayinclude a remote plasma source. A robot 406, at atmospheric pressure, isconfigured to move wafers from a cassette loaded through a pod 408 intoinbound load lock 402 via an atmospheric port 410. A wafer is placed bythe robot 406 on a pedestal 412 in the inbound load lock 402, theatmospheric port 410 is closed, and the load lock is pumped down. Wherethe inbound load lock 402 includes a remote plasma source, the wafer maybe exposed to a remote plasma treatment in the load lock prior to beingintroduced into a processing chamber 414. Further, the wafer also may beheated in the inbound load lock 402 as well, for example, to removemoisture and adsorbed gases. Next, a chamber transport port 416 toprocessing chamber 414 is opened, and another robot (not shown) placesthe wafer into the reactor on a pedestal of a first station shown in thereactor for processing. While the embodiment depicted in FIG. 4 includesload locks, it will be appreciated that, in some embodiments, directentry of a wafer into a process station may be provided.

The depicted processing chamber 414 includes four process stations,numbered from 1 to 4 in the embodiment shown in FIG. 4. Each station hasa heated pedestal (shown at 418 for station 1), and gas line inlets. Itwill be appreciated that in some embodiments, each process station mayhave different or multiple purposes. For example, in some embodiments, aprocess station may be switchable between an ALD and plasma-enhanced ALDprocess mode. Additionally or alternatively, in some embodiments,processing chamber 414 may include one or more matched pairs of ALD andplasma-enhanced ALD process stations. While the depicted processingchamber 414 includes four stations, it will be understood that aprocessing chamber according to the present disclosure may have anysuitable number of stations. For example, in some embodiments, aprocessing chamber may have five or more stations, while in otherembodiments a processing chamber may have three or fewer stations.

FIG. 4 depicts an embodiment of a wafer handling system 490 fortransferring wafers within processing chamber 414. In some embodiments,wafer handling system 490 may transfer wafers between various processstations and/or between a process station and a load lock. It will beappreciated that any suitable wafer handling system may be employed.Non-limiting examples include wafer carousels and wafer handling robots.FIG. 4 also depicts an embodiment of a system controller 450 employed tocontrol process conditions and hardware states of process tool 400.System controller 450 may include one or more memory devices 456, one ormore mass storage devices 454, and one or more processors 452. Processor452 may include a CPU or computer, analog and/or digital input/outputconnections, stepper motor controller boards, etc.

In some embodiments, system controller 450 controls all of theactivities of process tool 400. System controller 450 executes systemcontrol software 458 stored in mass storage device 454, loaded intomemory device 456, and executed on processor 452. Alternatively, thecontrol logic may be hard coded in the controller 450. ApplicationsSpecific Integrated Circuits, Programmable Logic Devices (e.g.,field-programmable gate arrays, or FPGAs) and the like may be used forthese purposes. In the following discussion, wherever “software” or“code” is used, functionally comparable hard coded logic may be used inits place. System control software 458 may include instructions forcontrolling the timing, mixture of gases, gas flow rates, chamber and/orstation pressure, chamber and/or station temperature, wafer temperature,target power levels, RF power levels, substrate pedestal, chuck and/orsusceptor position, and other parameters of a particular processperformed by process tool 400. System control software 458 may beconfigured in any suitable way. For example, various process toolcomponent subroutines or control objects may be written to controloperation of the process tool components used to carry out variousprocess tool processes. System control software 458 may be coded in anysuitable computer readable programming language.

In some embodiments, system control software 458 may includeinput/output control (IOC) sequencing instructions for controlling thevarious parameters described above. Other computer software and/orprograms stored on mass storage device 454 and/or memory device 456associated with system controller 450 may be employed in someembodiments. Examples of programs or sections of programs for thispurpose include a substrate positioning program, a process gas controlprogram, a pressure control program, a heater control program, and aplasma control program.

A substrate positioning program may include program code for processtool components that are used to load the substrate onto pedestal 418and to control the spacing between the substrate and other parts ofprocess tool 400.

A process gas control program may include code for controlling gascomposition (e.g., TMA, ammonia, and purge gases as described herein)and flow rates and optionally for flowing gas into one or more processstations prior to deposition in order to stabilize the pressure in theprocess station. A pressure control program may include code forcontrolling the pressure in the process station by regulating, forexample, a throttle valve in the exhaust system of the process station,a gas flow into the process station, etc.

A heater control program may include code for controlling the current toa heating unit that is used to heat the substrate. Alternatively, theheater control program may control delivery of a heat transfer gas (suchas helium) to the substrate.

A plasma control program may include code for setting RF power levelsapplied to the process electrodes in one or more process stations inaccordance with the embodiments herein.

A pressure control program may include code for maintaining the pressurein the reaction chamber in accordance with the embodiments herein.

In some embodiments, there may be a user interface associated withsystem controller 450. The user interface may include a display screen,graphical software displays of the apparatus and/or process conditions,and user input devices such as pointing devices, keyboards, touchscreens, microphones, etc.

In some embodiments, parameters adjusted by system controller 450 mayrelate to process conditions. Non-limiting examples include process gascomposition and flow rates, temperature, pressure, plasma conditions(such as RF bias power levels), pressure, temperature, etc. Theseparameters may be provided to the user in the form of a recipe, whichmay be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/ordigital input connections of system controller 450 from various processtool sensors. The signals for controlling the process may be output onthe analog and digital output connections of process tool 400.Non-limiting examples of process tool sensors that may be monitoredinclude mass flow controllers, pressure sensors (such as manometers),thermocouples, etc. Appropriately programmed feedback and controlalgorithms may be used with data from these sensors to maintain processconditions.

System controller 450 may provide program instructions for implementingthe above-described deposition processes. The program instructions maycontrol a variety of process parameters, such as DC power level, RF biaspower level, pressure, temperature, etc. The instructions may controlthe parameters to operate in-situ deposition of film stacks according tovarious embodiments described herein.

The system controller 450 will typically include one or more memorydevices and one or more processors configured to execute theinstructions so that the apparatus will perform a method in accordancewith disclosed embodiments. Machine-readable media containinginstructions for controlling process operations in accordance withdisclosed embodiments may be coupled to the system controller 450.

In some implementations, the system controller 450 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The system controller 450, depending on theprocessing conditions and/or the type of system, may be programmed tocontrol any of the processes disclosed herein, including the delivery ofprocessing gases, temperature settings (e.g., heating and/or cooling),pressure settings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the system controller 450 may be defined aselectronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the system controller 450 in the form ofvarious individual settings (or program files), defining operationalparameters for carrying out a particular process on or for asemiconductor wafer or to a system. The operational parameters may, insome embodiments, be part of a recipe defined by process engineers toaccomplish one or more processing steps during the fabrication of one ormore layers, materials, metals, oxides, silicon, silicon dioxide,surfaces, circuits, and/or dies of a wafer.

The system controller 450, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the system controller 450 may be in the “cloud” or all or apart of a fab host computer system, which can allow for remote access ofthe wafer processing. The computer may enable remote access to thesystem to monitor current progress of fabrication operations, examine ahistory of past fabrication operations, examine trends or performancemetrics from a plurality of fabrication operations, to change parametersof current processing, to set processing steps to follow a currentprocessing, or to start a new process. In some examples, a remotecomputer (e.g. a server) can provide process recipes to a system over anetwork, which may include a local network or the Internet. The remotecomputer may include a user interface that enables entry or programmingof parameters and/or settings, which are then communicated to the systemfrom the remote computer. In some examples, the system controller 450receives instructions in the form of data, which specify parameters foreach of the processing steps to be performed during one or moreoperations. It should be understood that the parameters may be specificto the type of process to be performed and the type of tool that thesystem controller 450 is configured to interface with or control. Thusas described above, the system controller 450 may be distributed, suchas by including one or more discrete controllers that are networkedtogether and working towards a common purpose, such as the processes andcontrols described herein. An example of a distributed controller forsuch purposes would be one or more integrated circuits on a chamber incommunication with one or more integrated circuits located remotely(such as at the platform level or as part of a remote computer) thatcombine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an atomic layer etch (ALE) chamber or module, an ionimplantation chamber or module, a track chamber or module, and any othersemiconductor processing systems that may be associated or used in thefabrication and/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the system controller 450 might communicate with one ormore of other tool circuits or modules, other tool components, clustertools, other tool interfaces, adjacent tools, neighboring tools, toolslocated throughout a factory, a main computer, another controller, ortools used in material transport that bring containers of wafers to andfrom tool locations and/or load ports in a semiconductor manufacturingfactory.

An appropriate apparatus for performing the methods disclosed herein isfurther discussed and described in U.S. patent application Ser. No.13/084,399 (now U.S. Pat. No. 8,728,956), filed Apr. 11, 2011, andtitled “PLASMA ACTIVATED CONFORMAL FILM DEPOSITION”; and Ser. No.13/084,305, filed Apr. 11, 2011, and titled “SILICON NITRIDE FILMS ANDMETHODS,” each of which is incorporated herein in its entireties.

The apparatus/process described herein may be used in conjunction withlithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels and the like. Typically, though not necessarily,such tools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallyincludes some or all of the following operations, each operation enabledwith a number of possible tools: (1) application of photoresist on aworkpiece, i.e., substrate, using a spin-on or spray-on tool; (2) curingof photoresist using a hot plate or furnace or UV curing tool; (3)exposing the photoresist to visible or UV or x-ray light with a toolsuch as a wafer stepper; (4) developing the resist so as to selectivelyremove resist and thereby pattern it using a tool such as a wet bench;(5) transferring the resist pattern into an underlying film or workpieceby using a dry or plasma-assisted etching tool; and (6) removing theresist using a tool such as an RF or microwave plasma resist stripper.

EXPERIMENTAL Experiment 1

Experiments were conducted to test deposition of silicon nitride usingdisilane and an ammonia plasma. Experiments were conducted at 250° C.and a pressure of 2 Torr. Each cycle included a 0.25 L dose of disilane,purge, 1 L exposure of ammonia with plasma for 2.5 seconds at varyingpowers, and another purge. In one trial, 500 cycles were performed; 200cycles were performed in the other trials. Nonuniformity and refractiveindex were measured for each trial. The results are shown in Table 1below.

TABLE 1 Silicon Nitride Deposition using Disilane and Ammonia PlasmaTrial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Power (W) 200 200 400600 1000 1000 Cycles 200 200 200 200 200 500 Avg Thickness (Å) 24 24 3738 46 43 Range Thickness (Å) 12 12 38 8 27 15 NU (%1 s) 5.6379 6.675130.8954 3.0193 10.146 5.5156 RI 2.1053 2.0769 1.8397 1.7683 1.75771.8342 RI NU (%1 s) 11.0532 8.8029 22.3947 14.8023 9.2469 8.8487 DepRate (Å/cyc) 0.12 0.12 0.18 0.19 0.23 0.09

Increasing the number of cycles and increasing the power (Trial 6)showed little change in average thickness, which suggests the initial 43Å of film is due to silicon surface nitridation, rather than filmgrowth. Thus, as shown in Table 1, there is little to no silicon nitridegrowth on the surface of the substrate, and the deposition is very low,while the thickness shown may be due to silicon surface nitridation.This experiment suggests that disilane and ammonia plasma alone areinsufficient to deposit silicon nitride films.

Experiment 2

An experiment was conducted to compare a silicon nitride film depositedusing disclosed embodiments versus using a conventional aminosilaneprecursor. First, a silicon nitride film was deposited using atomiclayer deposition (ALD). Bis(diethyl)aminosilane was introduced using anargon carrier gas to the station or chamber where the substrate washoused. The station was then purged. A nitrogen plasma was ignited at afrequency of 27 MHz and a power of 300 W for 2.5 seconds. The stationwas purged again. The deposited film deposited at about 0.46 Å of SiNper cycle.

Next, a silicon nitride film was deposited using ALD on anothersubstrate using the method described above in FIG. 1. Disilane wasintroduced using an argon carrier gas to a station where this secondsubstrate was housed. The station was then purged. A nitrogen plasma wasignited at a frequency of 27 MHz and a power of 300 W for 2.5 seconds.The station was purged again. The film deposition rate was about 0.55 Åper cycle. Both substrates were evaluated by x-ray photoelectronspectroscopy. The film deposited using aminosilane had 12% carbon. Thefilm deposited using disilane had 0% carbon.

Fourier transform spectroscopy was used to compare compositions of thetwo films. FIG. 5 shows the FTIR spectrum. Curve 503 represents the filmdeposited using the aminosilane precursor, which shows a Si—H peak at507, and some carbon peaks at 509. Curve 501 represents the filmdeposited using the disilane precursor, which shows a strong peak 505for the Si—N bond. Note that curve 503 has a smaller peak for the Si—Nbond, and that curve 501 has no corresponding peak for Si—H. Theseresults suggest that using the disilane precursor results in a film withmore Si—N bonds and cross-linking, essentially no carbon contamination,and little hydrogen incorporation.

Data for the above described films are represented below in Table 2 asFilm 1 (aminosilane precursor) and Film 3 (disilane precursor).Additional films were deposited at varying frequencies and powers. Inparticular, the bis(diethyl)aminosilane precursor was used to deposit anSiN film at a frequency of 13.56 MHz and a power of 300 W, the resultsof which are depicted in Film 2 of Table 2 below. Disilane was used as aprecursor for deposition at 300 W and 13.56 MHz, as well as 200 W and13.56 MHz. For each of these films, the deposition rate, uniformity, RI,peak height of Si—H (which represents incorporation of hydrogen), peakheight of Si—N (which represents presence of Si—N bonds), and stepcoverage were evaluated. For some films, some properties were notmeasured and are represented with the label “N/D” for no data. Overall,step coverage was similar between films deposited bybis(diethyl)aminosilane (28%, 33%) and disilane (27%). The filmsdeposited using disilane had improved RI and better film quality (lessSi—H, more Si—N, more uniform).

TABLE 2 Silicon Nitride Films Deposited by Bis(diethyl)aminosilane andDisilane Film # 1 2 3 4 5 Precursor bis(diethyl)aminosilane disilanePower (W) 300 300 200 Frequency 27 13.56 27 13.56 13.56 (MHz) Deposition0.44 0.5 0.55 0.60 0.55 Rate (Å/cyc) Uniformity 3.5% 2.5% 1.0% 1.0% 1.4%(1σ %) Refractive 1.89  1.83 1.98 1.89 1.95 Index Peak Height 3.4E−052.7E−05 0 N/D N/D Si—H Peak Height 7.4E−05 6.6E−05 1.3E−04 N/D N/D Si—NStep Coverage  28%  33% N/D  27% N/D

Experiment 3

An experiment was conducted to compare films deposited by ammonia plasmaversus nitrogen plasma. The first film was deposited at 400° C. usingtrisilylamine as the silicon precursor and ammonia plasma at an RFfrequency of 13.56 MHz. The second film was deposited at 400° C. usingtrisilylamine as the silicon precursor and nitrogen plasma at an RFfrequency of 13.56 MHz in accordance with the method described above inFIG. 1. The third film was deposited at 250° C. using trisilylamine asthe silicon precursor and ammonia plasma at an RF frequency of 13.56MHz. The fourth film was deposited at 250° C. using trisilylamine as thesilicon precursor and nitrogen plasma at an RF frequency of 13.56 MHz inaccordance with the method described above in FIG. 1. The depositionrates and RI values were evaluated for all films, and step coverage forthe two nitrogen plasma films was also measured. The results aresummarized in Table 3.

As shown, higher temperature resulted in higher step coverage, as Film 7has 60% step coverage, while Film 9 deposited at 250° C. has 30% stepcoverage. Moreover, the presence of hydrogen in the plasma suppresseddeposition. At 400° C., Film 6 had a lower deposition rate than Film 7,which was deposited using nitrogen plasma. The same pattern is shown forFilms 8 and 9, with Film 9 having a higher deposition rate when anitrogen plasma is used. These results suggest using nitrogen plasma asopposed to ammonia plasma increases deposition of the silicon nitridefilm.

TABLE 3 Ammonia Plasma vs. Nitrogen Plasma Film # 6 7 8 9 Precursortrisilylamine trisilylamine Frequency 13.56 13.56 (MHz) Temperature 400400 250 250 (° C.) Plasma Reactant Ammonia Nitrogen Ammonia Nitrogen(NH₃) (N₂) (NH₃) (N₂) Deposition Rate 0.21 0.45 0.06 0.27 (Å/cyc)Refractive Index 1.89 1.93 1.88 1.93 Step Coverage N/D 60% N/D 30%

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

1. A method of depositing a silicon nitride film on a substrate in achamber, the method comprising: (a) exposing the substrate to asilicon-containing precursor under conditions allowing formation of anadsorbed layer of the silicon-containing precursor on the substratesurface, and (b) exposing the adsorbed layer to a nitrogen (N₂) plasmato thereby form a silicon nitride film, wherein the silicon-containingprecursor is N—H bond-free and halogen-free.
 2. (canceled)
 3. The methodof claim 1, wherein the silicon-containing precursor is carbon-free. 4.The method of claim 1, wherein process temperature is less than about250° C.
 5. The method of claim 1, wherein the silicon-containingprecursor is selected from the group consisting of silane, disilane,trisilane, tetrasilane, and trisilylamine.
 6. The method of claim 1,further comprising: (c) repeating (a)-(b), and (d) periodically exposingthe substrate to a hydrogen-containing plasma.
 7. The method of claim 6,wherein the substrate is exposed to the hydrogen-containing plasma for atime between about 0.05 seconds and about 60 seconds.
 8. The method ofclaim 6, wherein exposing the substrate to the hydrogen-containingplasma comprises exposing the substrate to a hydrogen-containing gas andigniting a plasma, wherein the hydrogen-containing gas is selected fromthe group consisting of ammonia, hydrogen, and combinations thereof. 9.The method of claim 1, wherein a carrier gas is flowed throughout (a)through (b).
 10. The method of claim 9, wherein the carrier gas ishydrogen-free.
 11. The method of claim 1, wherein the frequency of theplasma is at least about 13.56 MHz.
 12. The method of claim 11, whereinthe frequency of the plasma is about 27 MHz.
 13. The method of claim 1,wherein the silicon-containing precursor is adsorbed onto less thanabout 60% of the substrate surface.
 14. The method of claim 1, whereinthe adsorbed layer on the substrate surface in (a) is less than about0.5 Å thick.
 15. The method of claim 1, wherein the silicon-containingprecursor has a silicon to hydrogen ratio between about 12:4 and about12:5.
 16. A method of depositing a silicon nitride film on a substratein a chamber, the method comprising: (a) exposing the substrate to asilicon-containing precursor under conditions under conditions allowingformation of an adsorbed layer of the silicon-containing precursor onthe substrate surface, and (b) exposing the adsorbed layer to a nitrogen(N₂) plasma to thereby form a silicon nitride film, wherein thesilicon-containing precursor comprises at least about 75% nonpolarcovalent bonds, and wherein the silicon-containing precursor ishalogen-free.
 17. The method of claim 16, wherein the silicon-containingprecursor is trisilylamine.
 18. The method of claim 16, furthercomprising: (c) repeating (a)-(b), and (d) periodically exposing thesubstrate to a hydrogen-containing plasma.
 19. The method of claim 18,wherein the substrate is exposed to the hydrogen-containing plasma for atime between about 0.05 seconds and about 60 seconds.
 20. The method ofclaim 18, exposing the substrate to the hydrogen-containing plasmacomprises exposing the substrate to a hydrogen-containing gas andigniting a plasma, wherein the hydrogen-containing gas is selected fromthe group consisting of ammonia, hydrogen, and combinations thereof. 21.The method of claim 16, wherein the adsorbed layer on the substratesurface in (a) is less than about 0.5 Å thick.